Aircraft, such as commercial airliners, typically include an environmental control system that provides the pressurization of a passenger cabin, as well as the supply of air to the passenger cabin during flight. The environmental control system utilizes air drawn from within the compressor section of at least one gas turbine engine on the aircraft to provide the necessary pressurization to the passenger cabin.
A typical gas turbine engine utilizes a compressor section, with multiple sequential compressors, to compress air and provides the compressed air to a combustor where the compressed air is mixed with fuel and ignited. The resultant gasses are expanded through a series of sequential turbines in a turbine section, with the expansion of the gasses driving the turbines to rotate.
Current engine designs include a high pressure bleed drawing air from the high pressure compressor and providing the air to the environmental control system. Also included in the typical designs is a second, low pressure bleed, connected to the lower pressure compressor and providing low pressure air to the environmental control system. Extracting air from the high pressure compressor carries a larger efficiency penalty than extracting air from the low pressure compressor.